Method of making molds



Nov; 13,1945. E. H. WALLACE 2,388,776

NNNNNN OR Patented Nov. 13, 1945 assai-7s ME'rnon oF MAKING Moms Edward H. Wallace, Detroit, Mich., assignor to United States Rubber Company, New York, N. Y., a corporation of New Jersey Original application January 10, 1942, Serial No. 'f

426,337. Divided and this application February 26, 1944, Serial No. 524,026

(cris-ssl 2 Claims.

This invention relates to a method of making molds. More particularly it relates to method of making a, mold having a resilient surface layer and a layer of non-resilient material attached to the resilient layer for the purpose of supporting and maintaining the first named layer in a relfollows all the detailed formations on the master and provides a surface which is an accurate reverse replica of the master. One of the principal objections to this practice is that, after removal of the master, it is diflicult to maintain the accurate dimensions originally imparted to the rubber layer due to the resiliency of the rubber. I have found that by a special treatment whereby the exposed surface of the rubber layer could be formed with many irregularities that a solid substance, such as plaster of Paris, could be readily` attached to the rubber layer. Upon/hardening of the plaster of Paris, the rubber layerbecomes firmly attached thereto; thus, the original dimensions of the rubber layer are accurately preserved.

It is, therefore, among the objectsof my inl vention to provide a rigid backing interlocked .with flexible molding surface; to provide a rein-v forced flexible mold surface capable of retaining the accurate dimensions of the master; and to provide a mold which may be prepared economically and expeditiously. These and other objects and advantages will appear more fully in the following detailed description when considered in connection with the accompanying drawing in which:

Fig. 1 is a side elevational view of an original article or master, such as, a baseball which is illustrative as an article for reproduction; l

Fig. 2 is a side elevational view of the naster imbedded inv` means to permit a one-halfrepro-l duction;

Fig. 3 is a transversed view, in section, of the master supporting means, rubber surface layer and backing; v

Fig., 4 is a perspective view illustrating the iinished mold and comprising the rubber surface layer and backing;A

Fig. 5 is a. transversed view in section of the rubber surface layer and a replica of the original article;

Fig. 6 is a, side elevational view of the complete replica;

Fig. l is an enlarged detailed view, in section, of a, portion of the rubber surface layer illustrating a surface formation; and,

Fig. 8 is a transversed view, in section, illustrating a modification of' the application shown in Fig. 3.

With reference to the drawing, and inparticular to Fig. 1, I show an original article, or master I, in the form of a baseball. However, it is to be understood that the baseball is illustrated for exemplary purposes only and that various other articles or shapes may be substituted therefor. A baseball has been illustrated because of the ne detail required to obtain a reproduction thereof,`

particularly with reference to the stitching and the minute ydetails accompanying the stitching and the space thus formed by the marginal edges of thebaseball cover. In order to obtain a replica from the master I, it is general practice in cases Paris support 2, as shown in Fig. 2. The master I is suspended in the plaster of Paris while the plaster is in a fluid state, and the parting surface is formed as the plaster hardens, thus one-half of the master I projects from the support 2.

Directly upon the exposed surface of 'the master Y and the adjoining surface of the support 2 'is `coatings are applied in the same manner.

formed a layer 3 of resilient material, such as a rubber composition. Preferably, this layer is formed by spraying latex, or the equivalent artiflcial dispersion of rubber or rubber-like material, directly against the mold surface. In order to accomplish this, a, conventional spray gun is employed, and a layer of latex in the order of 1/64 inch When the rubber layer is formed over a master inv which there are little or no undercutting, the total thickness of the layer 3 may be on theorder of 11s inch. However, where the master includes undercuts and irregularities, the thickness of the layer 3 is increased to a point where the elasticity of the rubber will permit easy separation of the layer from the master. The following is an exa ample of a latex composition which may be used to form the layer 3:

After the layer l has been built .up to the desired thickness by the application of successive coats of latex, the outer surface of the layer is 15 treated so as to provide an extremely irregular texture. This is accomplished by spraying latex and a coagulant simultaneously. In such cases the spray gun nozzles are held together to direct the combined latex-coagulant at the surface of 2 the layer and at a distance of approximately 15 inches from the layer.v -As a result of the combined latex-coagulant spray, a treeing effect is produced in the form of a plurality of upstanding projections l (Fig. 1). These projections are readily formed to a length of from one-eighth inch to a quarter inch. After the projections have been formed, the position of the spray gun relativel to the layer i may be rotated over an angle up to 180 with the result that nodules l are formed on the outermost tips of the projections 4. These nodules or enlarged portions serve tofunction as a locking means with material subsequently applied against the cuter'surface of layer A3. After the layer lxtogether with its projections l and nodules I are formed, the layer is dried for a period of about ten hours at room temperature or about two hours at 140 F.

A backing material is next applied to the surface of the layer l. Preferably, this supporting material is in theform of a backing l of plaster of Paris cast directly against the surface of the layer .3 and.- allowed to harden thereagainst. After the plaster has set. the application of heat is desirable. As a result of the application of the plaster 8 to the layer l, the projections I and nodules formed on the exterior surface of layer '3 become embedded in the plaster 6 and are therefore rigidly adhered to the plaster.

Figure 8 illustrates a modification of the disclosure shown in Figure 3 and shows a backing material 'l in the formY of a metal of low melting point, such as, lead or solder, formed directly against the surface of the layer 3.' The metal may be applied directly to the layer I by casting or by spraying the metal against the surface; Y. In either case a rigid backing is formed which be.. comes interlocked with the layer l to maintain vthe resilient layer in a xed position, thus, establishing its dimensions accurately. 7

After the plaster backing I and the layer I are thoroughly dried, the backing 8 together with the layer 4is strippedr from' the master I. The rigid adherence between the backing and layer prevents any permanent distortion of the layer IA during the stripping operation and maintains the ing into the mold cavity, formed by the layer 3. a deposit 8 of an alloy having a low melting point. In such case the alloy, for example, Cerrobase," which is a lead bismuth alloy having a Y melting point of about 254 F., is cast in the cavity of the layer 3 with the result that a half replica is formed of the original master I, such as shown in Figure 6. This replica contains all the detail l and undercut portions that are characteristic of the original master I. It is to be understood that the mold, formed by the layer 3 and backing B may be employed as a finished mold within which finished products may be molded, providing that the product can be formed against the rubber layer without substantially deteriorating the rub. ber. An example of preferable materials are -plaster, plastics, or other substances that may be molded in a Aliquid state and subsequently solidied. This replica 8 may now be used in an elec- 0 troforming bath and a layer -of iron electrodepositing thereon after which the replica 8 is melted therefrom leaving acompleted iron mold having all the' detail characteristics of the original master. Having thus obtained an iron mold,

it may be used repeatedly in the formation oi' a replica of the original master of a composition whichis resilient, such as, rubber. While a .one-

half mold 4is illustrated, it is to be understood that the other half of the mold may be formed' 80 in substantially the same manner to produce a completed article such as the spherical baseball illustrated in Figure 1.

This application is a divisiomof my applica tion Serial No.426,33'1, filed January 10, 1942.

While I have shown and described a mold and method of making same. it is' to be understood that the invention is susceptible oi?I those modiing depositing a layer of resilient material froml an aqueous dispersion of such material vonto the surface of an article, spraying additional amounts of said dispersion and a coagulant therefor simultaneously on the exposed surface of the resilient layer to 'form a multiplicity of irregularly shaped-projections extending therefrom, varying the 'relative direction of thev dispersion and coagulant spray to form enlarged nodules at the tips of at least some of said projections, forming depositing a layer of rubber from a latex composition onto the' surface of an article, spraying vlatex and coagulant simultaneously on the exposed surface of the rubber layer to form a mullayer 3 in a position for convenient handling during subsequent operations. `Figure 4 illustrates the mold' after it is stripped from the master l.

While the backing l and the layer] completes the formation of the mold, itfis sometimes de- 'f aired toA providean iron mold having the identi- 'cal surface details as present in the rubber layer I. This can be accomplished by casting or' spray- 75' tiplicity of irregularly shaped projections extend- Aing therefrom,-varying-the relative direction of the latex and coagulant spray to form enlarged nodules at the tim of atleast some of said projections, forming a plaster of Paris backing on vthe rubber layer with vsaid projections and nodules being embedded in the plaster of Paris to lockthe backing to the rubber layer, and strip-Y y ping the united rubber layer and plaster of Paris backing from the article. V

' l EDWARD B. WALLACE. 

